[BUGFIX] Enable rootline / content access to sysfolders

Only disallow DOCTYPE_RECYCLER in rootline and cObj->checkPid(),
instead of disallowing DOCTYPE_SYSFOLDER.

This makes it possible to fetch content from sysfolder pages.

At the same time, a hard check on accessing sys folders is added
to TSFE.

Resolves: #18079
Resolves: #20933
Releases: master
Change-Id: Ieb54d139bc1e7fc489c35f70510800be8ff14fb9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64038


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>